Backyard Naturalist: Turkey Vultures’ ‘Kettling’ Prepares Them for Long Trip

Editor’s Note: Outdoors Writer Russ Mohney died Aug. 31. The loss is staggering. His writing and insight into the outdoors of Southwest Washington was unmatched. We will be publishing his popular column each week in the coming months from his abundant body of work created throughout the past decade for The Chronicle. This column was originally published Oct. 14, 2005.

By Russ Mohney / For The Chronicle

I met a couple of regular readers this week while shopping and we chatted for a few moments about the value of calling or e-mailing when something unusual occurs. Very often the things that happen in their neighborhood prove fascinating to observers around the region, and I’m always happy to hear from them. They should never, I assured them, be bashful about calling me; their sightings are often the true stuff of which these weekly reflections are made.

Earlier this week I heard from Bill Behrns out on the northern edge of the Edison District in Centralia. Through the magic of modern technology, both Bill and his wife were on the phone simultaneously as they reported a flock of perhaps 35 turkey vultures circling around the fields along the nearby Skookumchuck. The outcome of that conversation led to this week’s column and is certainly a case in point.

At first blush of curiosity, one would think that such a concentrated flock of big, ugly scavengers indicated either an immense herd of small animals had met an untimely fate or somebody’s pet elephant had used up its five-score-and-something years. Actually, turkey vultures — as well as black vultures, condors, and several African vultures — engage in a curious behavior known as “kettling.” Local vultures occasionally gather in hunting groups, also known as kettles, but most instances of such odd conduct is most often seen when the annual southward migration begins.

The common turkey vulture is a fascinating creature, but much about the morbid forager (often described as “loathsome” by casual observers) isn’t very well known. Because they are shy and tend to avoid people, some things are still a bit of a mystery. Kettling is one of those behaviors still under study.

As a rule, vultures don’t eat live animals, and will certainly not hurt pets or children. Contrary to popular belief, however, they will sometimes attack very young or helpless animals.

Turkey vultures have the best sense of smell of any vulture anywhere, and are often attracted by the scent of mercaptan, a gas produced by the beginning of decay of animal matter. They have excellent daylight vision and use both senses to locate the carrion on which they feed.

Sometimes, when things are slow, groups will gather and circle around together until they find something to eat.

During the final few weeks of summer and the first weeks of fall, Turkey vultures begin gathering in large numbers preparatory to the long flight to Central and South America where apparently enough pathetic little animals die regularly enough to provide a sufficient food source. It was this annual autumn ritual that the Behrnses observed and about which far too little is known.

Some behavioral biologists suggest that the birds ride favorable thermals to reach the high elevation needed to begin a long, gliding flight south.

The very long period of circular “kettling” however, is believed by some to be a period during which the members of each small flock learn to recognize each other and perhaps form a loose bond that will increase their cooperation and feeding success on the heroic flights that may cover 4,000 miles or more.

Any good observer can probably figure out the practical reasons for vultures to kettle in their nesting or hunting ranges. It’s a way that a flock can cooperatively see and smell potential — and sometimes scarce — food resources. But the reasons for uniform, harmonious, pre-migration kettling behaviors aren’t known much at all. When you see a big flight of vultures (called a “venue” in group terms) you’re free to figure out for yourself what they are doing and why, and nobody will say you’re wrong, in most cases.